Automatic sear



Sept. 28, 1954 E, M. HARVEY AUTOMATIC SEAR 2 Sheets-Sheet 1 Original Filed Feb. 11, 1949 Sept. 28, 1954 E. M. HARVEY 2,690,095 AUTOMATIC SEAR Original Filed Feb. 11. 1949 2 Sheets-Sheet 2 E1111 5' M Harvey Patented Sept. 28, 1954 AUTOMATIC SEAR Earle M. Harvey, Agawam, Mass, assignor to the United States of America as represented by the Secretary or: War

Original application February 11, 1949, Serial No. 75,921. Divided and this application April l, 1950, Serial No. 153,952

(Granted under Title 35, U. 5. Code (1952),

see. 25-6) The invention described herein may be maria-- factured and used or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to those firearms arranged to be selectively operated in either semi" automatic or full automatic fire and relates more particularly to an automatic sear for the firing mechanism thereof.

This application is a division of my copending application Serial No. 75,921 filed February 11, 1949.

The object of this invention is to provide in an automatic and semiautomatic firearm an improved automatic sear arranged to block the fall of a hammer until such time as the firearm bolt reaches a fully locked battery position.

The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanymg drawings in which:

Fig. 1 is a right side fragmentary view of the firearm showing the bolt in the locked battery position and the automatic sear in its hammer releasing position;

Fig. 2 is a longitudinal sectional View of the firearm showing the bolt in a recoiled position and the automatic sear in position to block the fall of the hammer;

Fig. 3 is a fragmentary detail view of the firing mechanism set for automatic fire and showing how the fall of the hammer is blocked by the automatic sear;

Fig. 4 is a perspective view of the automatic scar; and

Fig. 5 is a cross-sectional view taken along the line 5-5 in Fig. 1.

The firearm illustrated in Fig. 1 generally comprises a receiver 5, a barrel ll threadably secured to the forward end thereof, a reciprocating bolt 7 having a locking block 8 associated therewith in a manner more fully described in my aforementioned copending application, and a trigger housing 9 suitably secured to the underside of receiver 5.

Bolt 1 is arranged to be fully loci-zed in battery position when locking block 8 has been pivoted upwardly to the position indicated by the dotted outline thereof shown in Fig. 1. An operating slide 26 is operatively associated with locking block 8 by means of a camming lug 25. When locking block 3 is in its bolt locking position, slide 26 is in a full battery position.

A trigger 28 is pivotally secured in housing 9 by means of a transverse pin it. A primary sear i5 is pivotally associated ith trigger it and is arranged to retain a hamper $5- in its cocked position during semi-automatic lire when trigger 28 is held in its pulled firing position. Upon release of trigger a hammer spring rotates such trigger in a counterclockwise direction whereupon cocking engagement of hammer 35 is transferred from sear it to a lug on trigger it. Thus trigger 28 must be again pulled to initiate another cycle of semi-automatic However, as more fully described in copenc application Serial No. 164,578 filed May 25, 1959, a selector mechanism 53 having a depending sear engaging portion 55 is provided to pivot sear it rearwardly with respect to trigger 23 so that when hammer 35 is cooked by the recoiling move-- ment of bolt l and locking block 8, no engage-- ment of such hammer with sear t5 will take place. Thus when trigger 28 is pulled, automatic fire will ensue as long as cartridges as are pres nt within a magazine 88.

An automatic sear designated generally by numeral. Q3 is provided to hold hammer 35 substantially the cooked position in the absence of engagement thereof by either primary sear 5- or trigger 28. Sear it comprises a forwardly extending arm ltl which terminates in an upwardly projecting portion m2 and a rearwardly extending arm H13. Arms ml and H33 are spa ed apart as best shown in Fig. l by a cylindrical cross bar ill l having parallel slabbed surfaces on the top and bottom thereof as best shown at i Receiver 5 is provided with a transverse hole for rotatably mounting sear d3 thereto. A vertical passage it? extends downwardly from ho e H35 and serves to provide access for cross bar ii?- during assembly to and disassembly from root er When so assembled, arm Hi3 lies adjacent the inner wall surface of receiver 5 while a m it! lies along the outside surface thereof i. ii. the upwardly projecting portion lili? arranged. to engage in a longitudinal cam tracl: its formed along the underside of operating slide 26. Cars track: Hill extends from a point slightly iorw of the extreme rear end of slide it and termina adjacent a handle Hi9 projecting laterally there from. A camming shoulder H provided at the rear end of track E38 for a purpose to described.

A substantially U-shaped magazine guard H? is fixedly secured to the forward end of trigger housing 9 and serves to enclose magazine 88. A lug H2 projects laterally and outwardly from 55 guard I I l and is provided with a vertical counterbored hole H3. A bracket I I4 is suitably secured to the forward end of trigger housing 9 and above magazine guard I II and is provided with an outwardly projecting arm H5 so disposed that a counterbored hole IIB therein is spaced apart from counterbored hole H3 but in axial vertical alignment therewith. A plunger III extends through holes I I3 and H6 and a collar portion H8 thereon is arranged to seat against a shoulder II 9 formed by the counterbored portion of hole H6. A helical coil spring I20 surrounds P ger Ill and seats between the underside of collar portion H8 and the counterbored portion of hole H3. Thus the top end of plunger lII is constantly urged upwardly against a fiat surface IZI on the underside of forwardly extending sear arm IOI to rotate automatic sear 43 in a counterclockwise direction sothat upwardly projecting portion I 02 thereon engages in cam track I03. However when operating slide 20 approaches its last increment of movement into battery position, shoulder H in cam track I08 cams sear arm IOI downwardly against the bias of spring 20 thereby raising the other arm I03 out of the path of movement of a lug 42 formed on the right side of hammer 35.

Referring now to Fig. 1 of the drawings, there is shown the firing mechanism of this invention in position for semi-automatic fire. Bolt l is in locked battery position and operating slide 26 is also in its battery position. As a result, camming shoulder H0 on slide 26 has rotated automatic sear 43 so that the rear end of arm I03 is raised out of the path of movement of lug 32 on hammer 35 which is retained in a cocked position by trigger 20. Selector mechanism 53 is in its semiautomatic position and therefore out of contact with sear 45 thus allowing hammer spring BI to pivot sear up against the rear edge of trigger 28.

Assuming a cartridge ad to be chambered in barrel 0, trigger 28 is pulled thereby releasing hammer 35 from cocking engagement therewith. The energy stored up in hammer spring El during cocking rotates hammer 35 to discharge cartridge 84. Operating slide 26 is driven to the rear in the manner conventional to gas operated firearms and serves to unlock bolt I. During such unlocking movement of slide 26, the underside thereof has moved off the upwardly projecting portion I02 of sear arm IOI and has brought cam track I08 into position to be engaged by portion I02 under the bias of spring pressed plunger III. This rocking movement of automatic sear 43 brings the rear end of arm I03 into the path of movement of lug 42 on hammer 35. The recoil travel of bolt I rotates hammer 35 in a conventional manner to be first engaged by sear 05. Upto this time the action of the moving parts has been so rapid that the operator of the firearm has not had sufficient time to release trigger 28 from its pulled position. Upon doing so, however, sear 35 becomes disengaged from hammer 35 whereupon trigger 20 becomes engaged therewith. Should hammer 35 fail to engage either sear 45 or trigger 28 for any reason, prior to the termination of battery movement of operating slide 26, the rear end of arm I03 efiectively blocks the fall of hammer 35 by engaging lug l2 thereon. But when both slide 26 and bolt I reach battery position, automatic sear 03 is rendered inoperative in the manner previously described. Pulling of trigger 28 then initiates another cycle of operation.

When it is desired that the firearm operate as a fully automatic weapon, i. e., continue to fire as long as trigger 28 is held in the pulled posi* tion and cartridges are available for chamber-- ing in barrel 6, selector mechanism 53 is rotated clockwise of the position indicated in 1. The depending sear engaging portion 65 of selector mechanism 53 is thereby moved to rock sear l5 rearwardly away from a hammer engaging posi tion. Since trigger 28 remains pulled, automatic sear 03 here provides the means for retaining hammer 35 in its cocked position until bolt I is locked in battery position and slide 2% has completed its forward travel. If such automatic sear 43 were not available, hammer 35 would follow the counter-recdiling bolt I and consequently would lack sufiicient impact. force to discharge the chambered round 84.

It will be readily appreciated by those skilled in the art that the automatic sear 30 here described not only provides means during automatic fire for retaining a hammer in its cocked position until the firearm breech is locked but also pro vides safety means for preventing accidental fall of the hammer prior to locking of the bolt during semi-automatic fire.

I claim:

1. In an automatic and semi-automatic firearm having a receiver, a bolt, a locking block pivotally connected to said bolt, said bolt and said block slidably mounted in the receiver for reciprocable movement between a locked battery position and a recoil position, an operating slide slidably mounted to the receiver for reciprocable movement between a battery and a recoil posi tion, said slide being operatively connected to said locking block, a hammer pivotally mounted in the receiver for movement between a cooked and a fired position and arranged to be pivoted toward the cooked position by said locking block during recoil thereof, an automatic sear rotatably secured to the receiver, said sear having a forwardly projecting arm and a rearwardly project-- ing arm connected by a cross bar portion whereby said first mentioned aim lies adjacent the outer wall of the receiver and said second mentioned arm lies adjacent the inner wall thereof, said slide having a cam track, an upwardly projecting portion on said forwardly projecting sear arm arranged to engage in said cam track, said rammer having a lug on the right side thereof arranged to be engaged by the rear end of said rearwardly projecting sear arm, and cam means on said slide for rotating said forwardly projecting arm on said automatic sear out of engagement with said cam track at the conclusion of forward movement of said slide into battery position whereby said rearwardly extending sear arm is pivoted out of the path of movement of said hammer lug after said bolt and said locking block are in locked battery position.

2. The structure defined in claim '1 including a spring pressed plunger slidably mounted to the receiver for vertical upward movement against the underside of said forwardly projecting sear arm, and stop means for limiting the upward movement of said plunger.

References Cited in the file of this patent 

